1. Field of the Invention
The present invention relates generally to the process of transferring data in parallel with a plurality of data lines utilized in the interior of a computer or its associated equipment. More particularly, the invention relates to inverting data in accordance with an efficient majority decision in order to reduce the number of data-bit changes (the number of data transitions) in the case transferring signals in parallel through a plurality of data lines (buses, etc.).
2. Description of the Related Art
In the interior of a computer or its associated equipment, data transfer is performed in an extremely wide range and generally data signals are transferred and processed in parallel through a great number of data lines from the necessity of processing data in large quantities and at high speed. More specifically, when n data bits (where n is a natural number) are transferred, n data lines are prepared and n (n-system) data bits changing in a time series manner are transferred in parallel from a transmitter to a receiver through the n data lines.
The data bits changing in a time series manner make a transition between a logic 0 and a logic 1. Note that the discrimination between a logic 0 and a logic 1 is performing by treating a voltage less than a predetermined voltage as a logic 0 and a voltage greater than the predetermined voltage as a logic 1.
A set of data lines, which are prepared for transferring a plurality of data bits thus changing in a time series manner, form a data-transferring width in data transfer and is generally called a bus. The bus, as hardware, includes all signal-transferring media and wires that can transfer signals in a broad sense. In a narrow sense, the bus, as a set of wires, can also be grasped as a separable component (there are cases where it includes a connector, etc.) called an interface cable or the like.
It is well known that unnecessary radiation of electro-magnetic waves will arise when data is transferred. Therefore, attention has been paid to a possibility that unnecessary radiation will be an obstacle to other constituent elements in the interior of electronic equipment and an obstacle to peripheral electronic equipment. As a basic countermeasure on a hardware side for preventing unnecessary radiation such as this, there is an elaborate measure of individually setting a filter to each data line.
A measure such as this is collectively called an electro-magnetic interference (EMI) countermeasure and is a countermeasure to pass an allowable value (standard value) determined in specific groups and countries or in the world as a product or an entire system.
The reason why a measure is thus aimed primarily at data lines is that it is seen that EMI radiation often becomes a problem in the case where it arises from a bus or an interface cable serving as a set of data lines than in the case where it arises from internal circuitry. The reason, as also described later, is that an interface cable has a property that it serves as an antenna for EMI radiation and increases EMI radiation, as it becomes longer. In most cases, an interface cable or the like is a separable component for connecting apparatuses separated from each other, so the cable requires a certain degree of length so that it can be widely used.
Presently, the high-density of the hardware in a computer and its associated equipment has advanced, so the complexity is rapidly increasing. An increase in the number of data lines is closely related to this EMI radiation. Particularly, in liquid crystal displays (LCDs), a great number of pixels are disposed for the high density in a display, and in order to these pixels individually, a great number of data lines, such as source lines, gate lines and the like, are provided. Therefore, a total of data lines for realizing data transfer becomes extremely enormous.
FIG. 1 illustrates the constitution of an LCD module 10 employing thin film transistors (TFTs) as an example of an LCD. The digital data bus-clock 20 extending from a gate array 11 is elaborately connected to an X-driver (also called a data driver or a source driver) 30 and a Y-driver (also called a gate driver) 40, whereby a TFT on a pixel electrode specified by X and Y can be driven.
The gate array 11 in this example is also called an LCD controller 11 by the fact that it controls the supply of signals to these drivers. The LCD controller and the drivers, as hardware, are realized as internal logic devices internally wired, such as LSI circuits. In color LCDs, pixel electrodes are alternately required individually every three colors: red, green, and blue. For this reason, the number of data lines becomes extremely enormous.
In the case of an LCD module as hardware, there are cases where it includes not only a panel (in which a liquid crystal is interposed between two glass substrates) but also peripheral members such as a back light. Furthermore, there are cases where it includes up to connector terminals that are connected to a system. Therefore, the meaning of the term xe2x80x9cLCD modulexe2x80x9d is not to be limited to the constitution expressed in FIG. 1 but should be interpreted widely.
Incidentally, it is known that there are the following relations (a)-(c) (general properties) between data transfer and EMI radiation.
(a) When digital signals of the same waveform are sent on n interface cables, the EMI radiation becomes n times the case where the digital signal is sent on a single interface cable.
(b) EMI radiation is proportional to the frequency component of a signal and becomes stronger as the repetition of a signal becomes faster. For instance, in the case where a digital signal simply repeats a logic high, a logic low, (1010 as pulse display, H is high, L is low) a logic high, and a logic low, the strongest EMI radiation arises. This is because a change in data bits per unit time (in this example, 4 bits), which is sent in a time series manner, will arise most frequently.
(c) An interface cable serves as an antenna for EMI radiation and therefore increases EMI radiation, as the cable becomes longer. That is, an external portion extending as a cable and the length thereof become a problem.
With these relations (general properties) as a premise, a contrivance for reducing EMI radiation, particularly based on the relation of (b) (general property), can be divided into the following (A)-(G).
(A) Reduce the number of data-bit changes themselves during data transfer.
(B) Invert (or process) all or some of data bits in order to reduce the number of data-bit changes.
(C) Contrive a method of evaluating the number of data-bit changes.
(D) Simplify a method of evaluating the number of data-bit changes.
(E) Reduce unnecessary radiation by a reduction in the number of data-bit changes.
(F) Reduce power dissipation by a reduction in the number of the data-bit changes.
(G) Select a method of utilizing the evaluation result of the number of data-bit changes.
These contrivances of (A)-(G) will be examined one by one.
First, as a conventional technique regarding (A), there is Published Unexamined Patent Application No. 8-79312. This technique processes data bits in a time series manner with respect to specific data bits (in which 1, 0, 1, and 0 are alternately transferred) that are considered as the worst case that will cause unnecessary radiation, thereby reducing the number of data-bit changes. This technique exhibits effect under a specific condition without particularly adding a redundant inverting signal. However, there are cases where the result of data processing will have an adverse effect on a reduction in the number of data-bit changes. Although it is described that the case having an adverse effect can be avoided by addition of a redundant inverting signal, there is no description of how the case having an adverse effect is avoided by addition of a redundant inverting signal.
Here, a conventional technique regarding (B) inverts data bits so that the number of data-bit changes is minimized, and transfers the inverted data bits along with a redundant inverting signal. The effect of a reduction in the number of data-bit changes results in a reduction in unnecessary radiation (E). If a loss of heat is excluded from consideration, the reduction effect will also result in a reduction in power dissipation (F).
Incidentally, the evaluation of the number of data-bit changes is based on a majority decision. That is, n data bits sent in a time series manner are detected and the number of data bits changed is decided by majority. In other words, with respect to the data bits sent in parallel in a time series manner through data lines, whether or not there is a change (i.e., transition) between 0 and 1 is decided in parallel by majority.
The reason why such a majority decision is made is for obtaining the effect of inversion correction when data bits to be decided by majority are all inverted. That is, only when the number of data bits changed exceeds more than half, the entire data bits can be processed advantageously (so that the number of bit changes can be reduced) by inversion correction (i.e., in the case of 0, it is corrected to 1 and in the case of 1, it is corrected to 0). This can be easily understood from the previously described relation (A). If the significance of the inversion effect based on the result of a majority decision is directly described, the case where an advantageous decision is obtained as a result of a majority decision will mean the case where the number of bit changes can be reduced by inversion. Also, the case where an advantageous decision is not obtained as a result of a majority decision will mean the case where the number of bit changes cannot be reduced by inversion.
In the case where the number of data lines to be decided by majority is an even number, there is a possibility that the number of changed bits and the number of unchanged bits will be the same. In such a case, even when inversion is performed or even when inversion is not performed, the effect of inversion correction is the same. Therefore, inversion does not make sense. It may safely be said that this case will be effective when data bits are not inverted than when data bits are inverted.
Here, considering that the number of the data-transferring lines (n lines) of an LCD or the like is considerably increasing in recent years with an increase in the number of colors and an increase in resolution, it is not suitable to decide all of n data bits by a strict majority. The reason for this is that the data-transferring rate is generally required to be very fast. Also, in order for the entire flow not to be limited by the time required for the strict majority decision, n data bits have be decided within a very short time by the strict majority.
If the number of data lines is not great but small, then the number of data-bit changes will not become great as a whole. Therefore, there is a low possibility that unnecessary radiation will have to be suppressed by specially processing data.
However, as will be easily appreciated from the aforementioned relation (general property) (a), unnecessary radiation is increased (getting worse) in proportion to an increase in the number of n data lines. As a result, the situation becomes significant. Later, in order to make a majority decision in a short time, the decision circuit itself requires connections of a combination of n lines and will become huge, considering the number of lines mutually connected. As a result, it becomes difficult to make the decision circuit as a realistic circuit. To make matters worse, a huge decision circuit itself increases unnecessary radiation or power dissipation. Furthermore, there is a fear that an increase in the scale of circuitry will increase cost.
The present invention, as a solution for reducing EMI radiation, relates primarily to inverting data bits and thereby reducing the number of data-bit changes, as in the aforementioned (B). The objective of the present invention is to provide novel techniques with regard to a method of deciding the number of data-bit changes and a utilization method thereof, without making a majority circuit complicate.
First, in the present invention, in order to avoid a considerable increase in the size of a majority circuit, the data lines are specified as blocks. A redundant inverting signal is obtained from the result of the majority decision of data bit transitions and is utilized as inversion information. This inversion information indicates whether or not transferred data bits have actually been processed (inverted), i.e., whether or not data bits should be reproduced. The inversion information can be transferred and utilized through an additional data line.
Also, in the present invention, n data lines (n data bits) are divided into s blocks each having m data bits (where n=mxc3x97s and where m and s are natural numbers). A majority decision is performed on the s blocks and is again performed on the s outputs from the s blocks. In this manner, the majority circuit can be structurally simplified (D). Also, a very small-scale and high-speed decision circuit can be realized. As a result, the aforementioned effects (E) or (F) are obtainable at an actually realizable cost.
In addition, the result of a majority decision at a small block can be utilized in data inversion with respect to the data transfer in units of m data bits in the interior of an LCD controller, etc. That is, a preselection result as a small block can be used in an internal portion and a main selection result as n data bits can be used in an external portion.